We can speed-up the workflow using the parallel option of make -j (number-of-parallel-jobs) and using a divide-and-conquer strategy. Here, the targets 'list1_2' and 'list3_4' can be processed independently in parallel.

By using the internal 'Make' functions $(eval), $(call), $(shell) we can define a recursive method "recursive". This method takes two arguments which are the 0-based indexes of a VCF in the list of VCFs. Here is the Makefile:
Running the makefile: